New Construction South Dakota
ras_tyler
| Posted in General Questions on
Next fall we will be building a new house in South Dakota, climate zone 6. I’m not looking for a passive house, just want to build the most efficient house we can, without blowing the bank. It will be a 2 story slab on grade. I plan on doing hydronic radiant floor heat. My question is what is the best wall assembly? As it stands now I’m thinking of going 2×6, with, blown in fiberglass, with 2” rigid foam, plywood sheathing with something of a rain screen before the siding. Any suggestions would be appreciated. Especially for the ceiling/roof.
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Replies
Ras,
If you build to the pretty-good-home standard, you are unlikely to benefit from radiant floor heat (which is expensive to install).
There is lots of good information here: https://www.greenbuildingadvisor.com/article/how-to-do-everything. This one (https://www.greenbuildingadvisor.com/article/how-to-design-a-wall) is specific to wall design.
Why won’t I benefit from the radiant floor heat? I will be installing, so the install won’t be expensive.
Typical well insulated houses don't have enough heat load to ever get the warm toes feel from floor heat. I went for floor heat for my home, since the place already had water heat but if I had to install from scratch, I would skip it and save the $10k to $20k. About the only time the floor feels warmish is in the dead of winter under my windows. The rest of the time, the you can only feel warmth in the tiled floor of the bathroom.
If you are in an area where summer AC is needed, it doesn't make sense to have two separate systems in the house. Go for a cold climate heat pump instead for both heating and cooling.
If you don't need AC, there could be an argument for low cost hydronic with something like panel rads. If your house low enough load that you can run off your hot water tank through a plate heat exchanger, the costs are significantly less especially if you can DIY.
As for walls, your assembly should work well enough. You might need an extra 1/2" to 1" of foam if you want to skip your interior vapor barrier see here for proper ratios:
https://www.buildingscience.com/documents/building-science-insights/bsi-100-hybrid-assemblies
As for roof insulation, you can't beat loose fill. Design your roof to be simple, make sure it can be easily vented and lowish slope for any cathedral ceilings so you can simply loose fill to R60.
P.S. Heated floors in bathrooms are great, I would definitely install it even if resistance mat. I sometimes keep mine running into the start of the cooling season here.
Ras,
It's hard to beat a simple vented gable roof with raised heel trusses and blown in insulation, for ease of construction, efficiency and lack of problems.
Those links Steve posted are well worth a look.
To benefit from hydronic heat in the floor design for a water temp in the 85 to 105 range. Zone the system so you can keep different spaces at different temperatures. I run our hydronic heat with a heat exchanger off the hot water tank to eliminate short cycling.